1. Field
The present invention generally relates to wireless communication systems. More particularly, the invention relates to a method and apparatus for regulating base station transmission power in a wireless communication system.
2. Background
In a digital wireless communications network, mobile stations exchange voice and packet data with base stations that are dispersed over a wide geographical area. Voice data concerns voice telephone calls and packet data relates to messages involved in surfing the Internet, delivering e-mail, and the like. There are still further channels dealing with text messaging (for example “short messaging service”) as well as various other services.
This information exchange is conducted over a variety of different forward and reverse link channels of the wireless communication network. Each channel is defined by a combination of physical and logical parameters. A forward link concerns communications from base stations to mobile stations, and reverse link concerns communications in the opposite direction. In networks of certain architectures, such as some releases of CDMA 2000, each mobile station receives forward link packet data from a single base station called the “serving” base station. The mobile station, however, transmits reverse link packet data to multiple base stations within range. Each intended base station, namely each of these base stations that is in the mobile's “active set,” separately acknowledges the data with a positive acknowledgement message (ACK) after receiving reverse link data from the mobile station correctly, or with a negative acknowledgement (NAK) after receiving reverse link data from the mobile station with error.
Setting the transmit power level for this ACK/NAK message can be a particular challenge. If the transmit level for the ACK/NAK message is too high, the base station unnecessarily wastes power, and further risks degrading other unrelated communications by bleed-over or other interference. Conversely, if the transmit level for the ACK/NAK message is too low, the mobile station may not receive it correctly, causing the mobile station to improperly respond to the ACK/NAK by submitting an incorrect response to the base station. Some undesirable results of this include consuming more of the mobile's limited battery power, wasting reverse link capacity, and increasing communication latency.
In the case of reverse link packet data communications received at the serving base station, setting the transmit power level for ACK/NAK messages is typically easier. Namely, message protocol dictates that mobiles send their serving base station a channel quality message. In the CDMA-2000 architecture, this message is sent on the reverse link channel quality indicator channel (R-CQICH). The channel quality message assesses the forward link channel quality from the serving base station to the mobile station. Thus, the serving base station can readily select the transmit power level of ACK/NAK messages to a given mobile by utilizing channel quality messages from that mobile as feedback.
As for non-serving base stations, however, there is no such feedback. Only the serving base station provides forward link packet data to the mobile station. Accordingly, the mobile station only provides forward link channel quality data to the serving base station. Yet, the non-serving base stations still receive reverse link packet data from mobiles, and acknowledge such receipt. Thus, the non-serving base stations set transmit power of their ACK/NAK messages in the “blind.” If the power level turns out to be excessive, the base station unnecessarily wastes power, and further risks degrading other unrelated communications by bleed-over or other interference. If the ACK/NAK transmit level is too low, the mobile station may not receive it correctly, in which case the mobile could send the base station a response that is inappropriate to the ACK/NAK message that the base station actually transmitted. This may undesirably consume more of the mobile's limited battery power, waste the reverse link capacity, and increase the communication latency.